This application relates generally to rotary machines and more particularly, to methods and apparatus for sealing a rotary machine.
At least some known rotary machines such as, but not limited to steam turbines and gas turbines, include a plurality of seal assemblies in a steam-flow path or an airflow path to facilitate increasing operating efficiency of the rotary machine. At least some known seal assemblies are positioned between a stationary component and a rotary component and/or between a high-pressure area and a low-pressure area. For example, to facilitate thrust balancing, a turbine rotor may be sealed relative to a cooperating stator to facilitate maintaining a higher pressure in a forward direction of the rotor as compared to a lower pressure in an aft direction of the rotor.
At least some known seal assemblies include seals such as, but not limited to, brush seals, leaf seals, and/or shingle seals. Known leaf and shingle seals include an array of multi-layered flexible plates, known as leaf plates, which are aligned and inclined in a circumferential direction about a central rotational axis of a rotary component. More specifically, the leaf plates are generally arranged to engage and disengage the rotor or rotary component during various operating stages of the rotary machine. For example, during shut down of the turbine engine, leaf tips of the leaf plates are generally in contact with a rotary component. During rotation of the rotary component, various forces generally act on the leaf plates to cause upward and downward deflection of the plates. Such forces include, but are not limited to, leaf/rotor contact forces, hydrodynamic lifting forces, and differential pressure forces. Leaf/rotor contact forces are generated by an initial contact between the leaf plate and the rotary component. Hydrodynamic lifting forces are generated by rotation of the rotary component. Differential pressure forces include differential pressure lifting forces and radially inward blow-down forces that are generated by differential pressure changes, a weight of the leaf plate, and/or an inclination of the leaf plate. Because a negligible amount of clearance between leaf tips and the rotary component facilitates reducing wearing of the leaf plates, a balance or leveraging between such forces acting on the leaf plates is desirable to ensure that the leaf tips are disengaged from the rotary component during rotor rotation.
At least some known seal assemblies include seal housing and an adjustable clearance control mechanism that is coupled to the stationary component. The seal housing includes at least a high-pressure-side front wall that is separated from a low-pressure-side back wall by a fixed gap that is set by the manufacturer. The clearance control mechanism actuates the seal housing including the leaf plates to adjust a clearance between leaf tips and a rotary component.
Such seal assemblies are used to reduce air leakage through the clearance and maintain a differential pressure between various machine components by radially actuating the leaf plates. However, within such seals, the high-pressure-side front wall and the low-pressure-side back wall of the seal housing generally experience substantially no pressure drop. Rather, a pressure drop is mainly experienced by leaf plates of the seal assembly. Therefore, any adjustment of the seal housing including the leaf plates generally requires a mechanism that can overcome extreme forces such as, but not limited to, differential pressure forces and frictional forces. Because of radial adjustments to the seal assembly, known clearance control mechanisms may reduce the seal assembly life and increase the overall maintenance cost of the machine.